513. Desmids and Diatomes, which are microscopic one-celled plants of the same cla.s.s, conjugate in the same way, as is shown in a Closterium by Fig. 566, 567. Here the whole living contents of two individuals are incorporated into one spore, for a fresh start. A reproduction which costs the life of two individuals to make a single new one would be fatal to the species if there were not a provision for multiplication by the prompt division of the new-formed individual into two, and these again into two, and so on in geometrical ratio. And the costly process would be meaningless if there were not some real advantage in such a fresh start, that is, in s.e.xes.

[Ill.u.s.tration: Fig. 568. Early stage of a species of Botrydium, a globose cell. 569, 570. Stages of growth. 571. Full-grown plant, extended and ramified below in a root-like way. 572. A Vaucheria; single cell grown on into a much-branched thread; the end of some branches enlarging, and the green contents in one (_a_) there condensed into a spore. 573. More magnified view of _a_, and the mature spore escaping.

574. Bryopsis plumosa; apex of a stem with its branchlets; all the extension of one cell. Variously magnified.]

514. There are other Algae of the gra.s.s-green series which consist of single cells, but which by continued growth form plants of considerable size. Three kinds of these are represented in Fig. 568-574.

515. =Lichens=, Latin _Lichenes_, are to be studied in the works of the late Professor Tuckerman, but a popular exposition is greatly needed.

The subjoined ill.u.s.trations (Fig. 575-580) may simply indicate what some of the commoner forms are like. The cup, or shield-shaped spot, or k.n.o.b, which bears the fructification is named the _Apothecium_. This is mainly composed of slender sacs (_Asci_), having thread-shaped cells intermixed; and each ascus contains few or several spores, which are commonly double or treble. Most Lichens are flat expansions of grayish hue; some of them foliaceous in texture, but never of bright green color; more are crustaceous; some are wholly pulverulent and nearly formless. But in several the vegetation lengthens into an axis (as in Fig. 580), or imitates stem and branches or threads, as in the Reindeer-Moss on the ground in our northern woods, and the Usnea hanging from the boughs of old trees overhead.

[Ill.u.s.tration: Fig. 575. A stone on which various Lichens are growing, such as (pa.s.sing from left to right) a Parmelia, a Sticta, and on the right, Lecidia geographica, so called from its patches resembling the outline of islands or continents as depicted upon maps. 576. Piece of thallus of Parmelia conspersa, with section through an apothecium. 577.

Section of a smaller apothecium, enlarged. 578. Two asci of same, and contained spores, and accompanying filaments; more magnified. 579. Piece of thallus of a Sticta, with section, showing the immersed apothecia; the small openings of these dot the surface. 580. Cladonia coccinea; the fructification is in the scarlet k.n.o.bs, which surround the cups.]

516. =Fungi.= For this immense and greatly diversified cla.s.s, it must here suffice to indicate the parts of a Mushroom, a Sphaeria, and of one or two common Moulds. The true vegetation of common Fungi consists of slender cells which form what is called a _Mycelium_. These filamentous cells lengthen and branch, growing by the absorption through their whole surface of the decaying, or organizable, or living matter which they feed upon. In a Mushroom (Agaricus), a k.n.o.bby ma.s.s is at length formed, which develops into a stout stalk (_Stipe_), bearing the cap (_Pileus_): the under side of the cap is covered by the _Hymenium_, in this genus consisting of radiating plates, the gills or _Lamellae_; and these bear the powdery spores in immense numbers. Under the microscope, the gills are found to be studded with projecting cells, each of which, at the top, produces four stalked spores. These form the powder which collects on a sheet of paper upon which a mature Mushroom is allowed to rest for a day or two. (Fig. 581-586.)

517. The esculent Morel, also Sphaeria (Fig. 585, 586), and many other Fungi bear their spores in sacs (asci) exactly in the manner of Lichens (515).

[Ill.u.s.tration: Fig. 581. Agaricus campestris, the common edible Mushroom. 582. Section of cap and stalk. 583. Minute portion of a section of a gill, showing some spore-bearing cells, much magnified.

584. One of these, with its four spores, more magnified.]

[Ill.u.s.tration: Fig. 585. Sphaeria rosella. 586. Two of the asci and contained double spores, quite like those of a Lichen; much magnified.]

518. Of the Moulds, one of the commoner is the Bread-Mould (Fig. 587).

In fruiting it sends up a slender stalk, which bears a globular sac; this bursts at maturity and discharges innumerable spores. The blue Cheese-Mould (Fig. 588) bears a cl.u.s.ter of branches at top, each of which is a row of naked spores, like a string of beads, all breaking apart at maturity. Botrytis (Fig. 589), the fruiting stalk of which branches, and each branch is tipped with a spore, is one of the many moulds which live and feed upon the juices of other plants or of animals, and are often very destructive. The extremely numerous kinds of s.m.u.t, rust, mildew, the ferments, bacteria, and the like, many of them very destructive to other vegetable and to animal life, are also low forms of the cla.s.s of Fungi.[1]

[Ill.u.s.tration: Fig. 587. Ascophora, the Bread-Mould. 588. Aspergillus glaucus, the mould of cheese, but common on mouldy vegetables. 589. A species of Botrytis. All magnified.]

FOOTNOTES:

[1] The "Introduction to Cryptogamous Botany," or third volume of "The Botanical Text Book," now in preparation by the author's colleague, Professor Farlow, will be the proper guide in the study of the Flowerless Plants, especially of the Algae and Fungi.

SECTION XVIII. CLa.s.sIFICATION AND NOMENCLATURE.

519. Cla.s.sification, in botany, is the consideration of plants in respect to their kinds and relationships. Some system of Nomenclature, or naming, is necessary for fixing and expressing botanical knowledge so as to make it available. The vast multiplicity of plants and the various degrees of their relationship imperatively require order and system, not only as to _names_ for designating the kinds of plants, but also as to _terms_ for defining their differences. Nomenclature is concerned with the names of plants. Terminology supplies names of organs or parts, and terms to designate their differences.

-- 1. KINDS AND RELATIONSHIP.

520. Plants and animals have two great peculiarities: 1st, they form themselves; and 2d, they multiply themselves. They reproduce their kind in a continued succession of

521. =Individuals.= Mineral things occur as _ma.s.ses_, which are divisible into smaller and still smaller ones without alteration of properties. But organic things (vegetables and animals) exist as _individual beings_. Each owes its existence to a parent, and produces similar individuals in its turn. So each individual is a link of a chain; and to this chain the natural-historian applies the name of

522. =Species.= All the descendants from the same stock therefore compose one species. And it was from our observing that the several sorts of plants or animals steadily reproduce themselves, or, in other words, keep up a succession of similar individuals, that the idea of species originated. There are few species, however, in which man has actually observed the succession for many generations. It could seldom be proved that all the White Pine trees or White Oaks of any forest came from the same stock. But observation having familiarized us with the general fact that individuals proceeding from the same stock are essentially alike, we infer from their close resemblance that these similar individuals belong to the same species. That is, we infer it when the individuals are as much like each other as those are which we know, or confidently suppose, to have sprung from the same stock.

523. Ident.i.ty in species is inferred from close similarity in all essential respects, or whenever the differences, however considerable, are not known or reasonably supposed to have been originated in the course of time under changed conditions. No two individuals are exactly alike; a tendency to variation pervades all living things. In cultivation, where variations are looked after and cared for, very striking differences come to light; and if in wild nature they are less common or less conspicuous, it is partly because they are uncared for.

When such variant forms are pretty well marked they are called

524. =Varieties.= The White Oak, for example, presents two or three varieties in the shape of the leaves, although they may be all alike upon each particular tree. The question often arises, and it is often hard to answer, whether the difference in a particular case is that of a variety, or is specific. If the former, it may commonly be proved by finding such intermediate degrees of difference in various individuals as to show that no clear distinction can be drawn between them; or else by observing the variety to vary back again in some of its offspring.

The sorts of Apples, Pears, Potatoes, and the like, show that differences which are permanent in the individual, and continue unchanged through a long series of generations when propagated by division (as by offsets, cuttings, grafts, bulbs, tubers, etc.), are not likely to be reproduced by seed. Still they sometimes are so, and perhaps always tend in that direction. For the fundamental law in organic nature is that offspring shall be like parent.

RACES are such strongly marked varieties, capable of coming true to seed. The different sorts of Wheat, Maize, Peas, Radishes, etc., are familiar examples. By selecting those individuals of a species which have developed or inherited any desirable peculiarity, keeping them from mingling with their less promising brethren, and selecting again the most promising plants raised from their seeds, the cultivator may in a few generations render almost any variety transmissible by seed, so long as it is cared for and kept apart. In fact, this is the way the cultivated domesticated races, so useful to man, have been fixed and preserved. Races, in fact, can hardly, if at all, be said to exist independently of man. But man does not really produce them. Such peculiarities--often surprising enough--now and then originate, we know not how (the plant _sports_, as the gardeners say); they are only preserved, propagated, and generally further developed, by the cultivator's skilful care. If left alone, they are likely to dwindle and perish, or else revert to the original form of the species. Vegetable races are commonly annuals, which can be kept up only by seed, or herbs of which a succession of generations can be had every year or two, and so the education by selection be completed without great lapse of time.

But all fruit-trees could probably be fixed into races in an equal number of generations.

BUD-VARIETIES are those which spring from buds instead of seed. They are uncommon to any marked extent. They are sometimes called _Sports_, but this name is equally applied to variations among seedlings.

CROSS-BREEDS, strictly so-called, are the variations which come from cross-fertilizing one variety of a species with another.

HYBRIDS are the varieties, if they may be so called,--which come from the crossing of species (331). Only nearly related species can be hybridized; and the resulting progeny is usually self-sterile, but not always. Hybrid plants, however, may often be fertilized and made prolific by the pollen of one or the other parent. This produces another kind of cross-breeds.

525. Species are the units in cla.s.sification. Varieties, although of utmost importance in cultivation and of considerable consequence in the flora of any country, are of less botanical significance. For they are apt to be indefinite and to shade off one form into another. But species, the botanist _expects_ to be distinct. Indeed, the practical difference to the botanist between species and varieties is the definite limitation of the one and the indefiniteness of the other. The botanist's determination is partly a matter of observation, partly of judgment.

526. In an enlarged view, varieties may be incipient species; and nearly related species probably came from a common stock in earlier times. For there is every reason to believe that existing vegetation came from the more or less changed vegetation of a preceding geological era. However that may be, species are regarded as permanent and essentially unchanged in their succession of individuals through the actual ages.

527. There are, at nearly the lowest computation, as many as one hundred thousand species of phanerogamous plants, and the cryptogamous species are thought to be still more numerous. They are all connected by resemblances or relationships, near and remote, which show that they are all parts of one system, realizations in nature, as we may affirm, of the conception of One Mind. As we survey them, they do not form a single and connected chain, stretching from the lowest to the highest organized species, although there obviously are lower and higher grades. But the species throughout group themselves, as it were, into cl.u.s.ters or constellations, and these into still more comprehensive cl.u.s.ters, and so on, with gaps between. It is this cl.u.s.tering which is the ground of the recognition of _kinds_ of species, that is, of groups of species of successive grades or degree of generality; such as that of similar species into _Genera_, of genera into _Families_ or _Orders_, of orders into _Cla.s.ses_. In cla.s.sification the sequence, proceeding from higher or more general to lower or special, is always CLa.s.s, ORDER, GENUS, SPECIES, VARIETY (if need be).

528. =Genera= (in the singular, _Genus_) are a.s.semblages of closely related species, in which the essential parts are all constructed on the same particular type or plan. White Oak, Red Oak, Scarlet Oak, Live Oak, etc., are so many species of the Oak genus (Latin, _Quercus_). The Chestnuts compose another genus; the Beeches another. The Apple, Pear, and Crab are species of one genus, the Quince represents another, the various species of Hawthorn a third. In the animal kingdom the common cat, the wild-cat, the panther, the tiger, the leopard, and the lion are species of the cat kind or genus; while the dog, the jackal, the different species of wolf, and the foxes, compose another genus. Some genera are represented by a vast number of species, others by few, very many by only one known species. For the genus may be as perfectly represented in one species as in several, although, if this were the case throughout, genera and species would of course be identical. The Beech genus and the Chestnut genus would be just as distinct from the Oak genus even if but one Beech and Chestnut were known; as indeed was once the case.

529. =Orders= are groups of genera that resemble each other; that is, they are to genera what genera are to species. As familiar ill.u.s.trations, the Oak, Chestnut, and Beech genera, along with the Hazel genus and the Hornbeams, all belong to one order. The Birches and the Alders make another; the Poplars and Willows, another; the Walnuts (with the b.u.t.ternut) and the Hickories, still another. The Apple genus, the Quince and the Hawthorns, along with the Plums and Cherries and the Peach, the Raspberry with the Blackberry, the Strawberry, the Rose, belong to a large order, which takes its name from the Rose. Most botanists use the names "Order" and "Family" synonymously; the latter more popularly, as "the Rose Family," the former more technically, as "Order _Rosaceae_."

530. But when the two are distinguished, as is common in zoology, Family is of lower grade than Order.

531. =Cla.s.ses= are still more comprehensive a.s.semblages, or great groups. Thus, in modern botany, the Dicotyledonous plants compose one cla.s.s, the Monocotyledonous plants another (36-40).

532. These four grades, Cla.s.s, Order, Genus, Species, are of universal use. Variety comes in upon occasion. For, although a species may have no recognized varieties, a genus implies at least one species belonging to it; every genus is of some order, and every order of some cla.s.s.

533. But these grades by no means exhaust the resources of cla.s.sification, nor suffice for the elucidation of all the distinctions which botanists recognize. In the first place, a higher grade than that of cla.s.s is needful for the most comprehensive of divisions, that of all plants into the two _Series_ of Phanerogamous and Cryptogamous (6); and in natural history there are the two _Kingdoms_ or _Realms_, the Vegetable and the Animal.

534. Moreover, the stages of the scaffolding have been variously extended, as required, by the recognition of a.s.semblages lower than cla.s.s but higher than order, viz. _Subcla.s.s_ and _Cohort_; or lower than order, a _Suborder_; or between this and genus, a _Tribe_; or between this and tribe, a _Subtribe_; or between genus and species, a _Subgenus_; and by some a species has been divided into _Subspecies_, and a variety into _Subvarieties_. Last of all are _Individuals_.

Suffice it to remember that the following are the princ.i.p.al grades in cla.s.sification, with the proper sequence; also that only those here printed in small capitals are fundamental and universal in botany:--

SERIES, CLa.s.s, Subcla.s.s, Cohort, ORDER, or FAMILY, Suborder, Tribe, Subtribe, GENUS, Subgenus or Section, SPECIES, Variety.

-- 2. NAMES, TERMS, AND CHARACTERS.

535. The name of a plant is the name of its genus followed by that of the species. The name of the genus answers to the surname (or family name); that of the species to the baptismal name of a person. Thus _Quercus_ is the name of the Oak genus; _Quercus alba_, that of the White Oak, _Q. rubra_, that of Red Oak, _Q. nigra_, that of the Black-Jack, etc. Botanical names being Latin or Latinized, the adjective name of the species comes after that of the genus.

536. =Names of Genera= are of one word, a substantive. The older ones are mostly cla.s.sical Latin, or Greek adopted into Latin; such as _Quercus_ for the Oak genus, _f.a.gus_ for the Beech, _Corylus_, the Hazel, and the like. But as more genera became known, botanists had new names to make or borrow. Many are named from some appearance or property of the flowers, leaves, or other parts of the plant. To take a few examples from the early pages of the "Manual of the Botany of the Northern United States,"--the genus _Hepatica_ comes from the shape of the leaf, resembling that of the liver. _Myosurus_ means mouse-tail.

_Delphinium_ is from delphin, a dolphin, and alludes to the shape of the flower, which was thought to resemble the cla.s.sical figures of the dolphin. _Xanthorrhiza_ is from two Greek words meaning yellow-root, the common name of the plant. _Cimicifuga_ is formed of two Latin words meaning to drive away bugs, i. e. Bugbane, the Siberian species being used to keep away such vermin. _Sanguinaria_, the Bloodroot, is named from the blood-like color of its juice. Other genera are dedicated to distinguished botanists or promoters of science, and bear their names: such are _Magnolia_, which commemorates the early French botanist, Magnol; and _Jeffersonia_, named after President Jefferson, who sent the first exploring expedition over the Rocky Mountains. Others bear the name of the discoverer of the plant; as, _Sarracenia_, dedicated to Dr.

Sarrazin, of Quebec, who was one of the first to send the common Pitcher-plant to the botanists of Europe; and _Claytonia_, first made known by the early Virginian botanist Clayton.

537. =Names of Species.= The name of a species is also a single word, appended to that of the genus. It is commonly an adjective, and therefore agrees with the generic name in case, gender, etc. Sometimes it relates to the country the species inhabits; as, Claytonia _Virginica_, first made known from Virginia; Sanguinaria _Canadensis_, from Canada, etc. More commonly it denotes some obvious or characteristic trait of the species; as, for example, in Sarracenia, our northern species is named _purpurea_, from the purple blossoms, while a more southern one is named _flava_, because its petals are yellow; the species of Jeffersonia is called _diphylla_, meaning two-leaved, because its leaf is divided into two leaflets. Some species are named after the discoverer, or in compliment to a botanist who has made them known; as, Magnolia _Fraseri_, named after the botanist Fraser, one of the first to find this species; and Sarracenia _Drummondii_, for a Pitcher-plant found by Mr. Drummond in Florida. Such personal specific names are of course written with a capital initial letter. Occasionally some old substantive name is used for the species; as Magnolia _Umbrella_, the Umbrella tree, and Ranunculus _Flammula_. These are also written with a capital initial, and need not accord with the generic name in gender.

Geographical specific names, such as _Canadensis_, _Caroliniana_, _Americana_, in the later usage are by some written without a capital initial, but the older usage is better, or at least more accordant with English orthography.